We explain what spermatogenesis is and the phases into which this process is divided. Also, what is azoospermia and oogenesis?
What is spermatogenesis?
It is called spermatogenesis or spermatocytogenesis when sperm generation or production process, which takes place inside the male sex glands (testes), specifically in the seminiferous tubules, coiled ducts of about 30 to 60 cm. in length and 0.2 mm in width. Between the two testicles of the man there are more than a thousand of these ducts.
Spermatozoa, as is known, are the gametes or male reproductive cells, endowed with half of the individual‘s genome (haploid or n) and self-mobility by means of a single flagellum (or tail). They are expelled from the body during ejaculation, along with the rest of the seminal content (semen) and, upon finding an ovum (female gamete) ready to be fertilized, they fuse to give rise to a new life.
The discovery of the cellular nature of sperm is relatively recent: it coincides with the discovery of the cell theory in the 19th century.
The word spermatozoon it was used for the first time in 1827, and as early as 1841 it was in frequent use, although they were not yet considered as reproductive cells. Years later, it would be Albert Koeliker who would offer the first complete explanation of the phenomenon, based on the seminal fluid of various animals.
Spermatogenesis is triggered in the human body by the release of the hormone GnRH (gonadotropin-releasing hormone), secreted by the hypothalamus; It consists of a successive process of mitosis and meiosis, and has an approximate total duration of between 62 and 75 days.
Phases of spermatogenesis
The creation of sperm involves the following phases:
- Proliferative or spermatogon phase. Type A spermatogonia are formed from germ stem cells: cells that by mitotic division (mitosis) give rise to type A and type B spermatogonia. The former will continue to replicate and produce both types of cells; the latter will instead divide into two primary spermatocytes, which in turn will divide into four mature spermatozoa. This first phase takes place in the man’s puberty, when his reproductive system is activated.
- Meiotic phase or spermatocytogenesis. In this phase, new mechanisms of cell division are produced, which give rise to haploid cells called spermatids, through meiosis processes. This occurs during two stages:
- Meiosis I. Each primary (diploid) spermatocyte divides into two secondary (haploid) spermatocytes.
- Meiosis II. Secondary spermatocytes divide into two spermatids (haploid), thus obtaining four cells from the first. In the latter, the shape of the mature sperm begins to take shape, and they even present a flagellum.
- Spermiogenesis. This last stage occurs during the maturation of the spermatid to form mature sperm. The flagellum grows to its ideal point, the cell acquires its characteristic pointed shape, the reduction of the cytoplasm, the elongation of its cell nucleus and the development of acrosome. At this time the sperm are released into the center of the seminiferous tubule, ready to be ejaculated.
Azoospermia
This is the name given to a disease of the human male reproductive system, consisting of the absence of sperm in male semen. This naturally minimizes the fertility levels of the individual.
This ailment can be determined by studies of semen quality, as well as hormonal analysis, since it is attributed to the deficiency of the hormone FSH (Follicle Stimulating Hormone), responsible, among others, for the testicle to produce sperm.
It should not be confused with aspermia, which is the complete lack of semen during ejaculation.
Oogenesis
Oogenesis is the equivalent process to spermatogenesis, but in the female reproductive system, that is, it is the process of formation and maturation of ovules (female gametes). In mammals, this process produces only a few hundred eggs during a woman’s fertile life, which occurs in her gonads, the ovaries.
This process is hormonally regulated by the pituitary gland, by means of the FSH hormone and the leutinizing hormone. Like spermatogenesis, this process involves different stages of mitosis and meiosis to finally produce haploid (n) sex cells from diploid (2n).